This invention relates to tufting machines and more particularly to an improved tufting machine for fine gauge tufting, having at least two transverse rows of needles and only one row of hooks or loopers to seize the yarn from the needles.
There is a continual effort in the tufting machine industry to produce machines that will operate faster, create patterns with a novel appearance, create patterns with a very fine gauge, create patterns with a minimum of yarn used in the backstitch, and create patterns of a uniform appearance which may both conceal irregularities in the yarn and reduce the necessity for further processing such as shearing to improve the finished carpets' appearance.
In order to further these goals, the tufting industry has devised a variety of improvements ranging from yarn feed control attachments to produce patterns and provide measured amounts of yarn for each stitch, to staggered needle bars to allow a finer gauge, shiftable needle bars to produce patterns and even multiple shiftable needle bars.
A staggered needle bar typically consists of two rows of needles extending transversely across the tufting machine. The rows of needles are generally spaced 0.25 inches apart in the longitudinal direction and are offset so that the needles in the rear transverse row are longitudinally spaced between the needles in the front transverse row. In operation the needle bar is reciprocated so that the needles penetrate and insert loops of yarn in a backing material fed longitudinally beneath the needles. The loops of yarn are seized by loopers or hooks moving in timed relationship with the needles beneath the fabric. In most staggered needle bar tufting machines, there are front loopers which cooperate with the front needles and rear loopers which cooperate with the rear needles. These loopers may be mounted in a single row with the front loopers being approximately 0.25 inches longer, in the case of a cut pile tufting machine, (or the rear loopers being longer in a loop pile machine) as shown in U.S. Pat. Nos. 4,067,270 and 4,519,326. One disadvantage to the longer front loopers in a cut pile tufting machine is that the front loopers will hold several more loops of yarn than the rear loopers and as a result will tend to back-rob a slightly different amount of yarn leading to a corn-rowing effect. This sometimes requires the cut pile carpet to be sheared to an even finish after tufting. Alternatively, in a loop pile machine, it may be possible to have two separate rows of loopers such as those illustrated in U.S. Pat. No. 4,841,886 where loopers in the front hook bar cooperate with the front needles and loopers in the rear hook bar cooperate with rear needles. Similar looper construction have been used in tufting machines with separate independently shiftable front and rear needle bars, so that there are specifically designated front loopers to cooperate with front needles and specifically designated rear loopers to cooperate with rear needles.
The result of having loopers co-operable with only a given row of needles on a fine gauge tufting machine with either a staggered needle bar or two independently shiftable needle bars is that it is only possible to move a particular needle laterally by a multiple of the gauge of the needles on the relevant needle bar. Thus for a fairly common 0.20 inch gauge row of needles with corresponding loopers set at 0.20 inch gauge, the needles must be shifted in increments of 0.20 inches. This is so even though in a staggered needle bar with two rows of 0.20 inch gauge needles the composite gauge of the staggered needle bar is 0.10 inch gauge. The necessity of shifting the rows of needles twice the gauge of the composite needle assembly results in patterns with less definition than could be obtained if it were possible to shift in increments of the composite gauge.
One effort to reduce the gauge of tufting has been to use smaller and more precise parts. For instance, Green, U.S. Pat. No. 4,519,326, is directed to an improved needle bar that was easier to manufacture and provided more accurate transverse needle gauge. The needle bars of this invention would typically consist of either single transverse row of needles or two staggered and longitudinally spaced transverse rows of needles. The usual longitudinal spacing between the two staggered rows of needles would be at least 0.1875 inches. Staggered needle bars according to U.S. Pat. No. 4,519,326 were intended for use on tufting machines with a backing fabric feed, a needle drive, either one or two rows of loopers (but if used with a single row of loopers, the loopers would have different length necks), and a needle bar shifting mechanism such as shown in Morgante, U.S. Pat. No. 4,829,917. The invention of U.S. Pat. No. 4,519,326 taught neither the close longitudinal spacing (less than 0.157 inches) of the two transverse rows of staggered needles, nor the use of a single row of loopers having necks of equal length so that the loopers could seize yarns from either transverse row of needles.
In order to overcome the problem of double gauge shifting, U.S. Pat. No. 5,224,434 suggests a tufting machine with front loopers spaced equal to the composite gauge and rear loopers spaced equal to the composite gauge. Thus on a tufting machine with two rows of 0.20 inch gauge needles there would be a row of front loopers spaced at 0.10 inch gauge and a row of rear loopers spaced at 0.10 inch gauge. Although this allows the shifting of each row of needles in increments equal to the composite gauge, this solution is limited in that the front needles can only be used to create loop pile and the rear needles can only be used to create cut pile.
An alternative arrangement is proposed in U.S. Pat. No. 5,193,472 where a single row of loopers can cooperate with either the row of needles on a front needle bar or the row of needles on a rear needle bar, the needle bars being closely positioned so that the rows of needles are longitudinally spaced about 0.125 inches apart, or a variation thereof in U.K. Patent Application 2255785A wherein the loopers can also cooperate with both rows of needles simultaneously. Although presenting a conceptual improvement, actual operation of such a tufting machine presents numerous practical difficulties which have not been addressed. For instance, when the looper crosses the first needle, it is deflected somewhat and when crossing the second needle it may split the yarn or fail to pick up the yarn entirely. Although in U.S. Pat. No. 3,443,534 a similar problem was solved by offsetting the second row of needles, when dealing with a 0.10 inch composite gauge tufting machine there is not sufficient space for such an offset. Furthermore, because the second row of needles is crossed later in the stitch cycle, the timing of the looper meeting the second needle is slightly altered. The use of conventional needle plates with fingers extending beneath the backing fabric and between the needles also tends to pinch the yarn resulting in irregularities in the finished carpet.
When originally developed in the 1970s, staggered needle bar cut pile tufting machines were used to produce some new carpet patterns. However, the types of patterns that could be produced by these machines were limited. Today, dual shiftable needle bar tufting machines and/or scroll attachments are generally used to tuft patterned carpet. At present, the primary use of staggered needle bar tufting machines is for the tufting of solid color carpets, often using relatively inexpensive yarns. Inexpensive yarns frequently contain streaks of lighter or darker color. By shifting a staggered needle bar threaded with a single color of yarns, the yarns from the first transverse row of needles will cross with the yarns from the second transverse row of needles and any streaks in a yarn will be tufted in rows with yarns from other needles so that streaking will not be apparent in the finished carpet. In tufting such a solid color carpet, pattern definition is of absolutely no concern.
Instead, some of the principal concerns are yarn savings, speed of operation, and better carpet finish. Each of these concerns is a problem or goal which has been long recognized in the tufting industry. Tufting machine purchasers and operators are always interested in reducing their raw material costs, gaining increased carpet output through faster machine operation, and minimizing blemishes on finished carpet such as corn rowing without the necessity of extra processing. The present invention addresses these concerns.